Peters



esteem HORACE I. CRANDALL, OF NEW BED-FORD, MASSACHUSETTS.

Letters Patent No. 83,469, dated October 27, 1868. l i l INIPROVEMENT INCOG-WHEELS AIE'OR. lG-EARING;

wb- L The Schedule referred to in these Lettere Patent and making partof the same.

The nature of my invention consists of three distinct features, which,in combination, will produce such a form of tooth (for double-facedteeth) that any two bf the saine pitch can run equally correct togetherin all their various positions.

To enable those skilled in the arts to apply my invention, I willproceed to describe the saine.

The rule for making the old English -system of teeth is to space off thethickness of the Vteeth on the pitchline or circle from the radialcentre-line of each tooth, then using the pitch for the radius forsweeping the faces of the teeth, the 'fixed leg ofthe compass restinguponV the pitch-line or circle, as represented in Figures l and .2,plate l. i Some makers have endeavored to overcome the eriors of theabove system by adopting a new radius and locus-centre line on `whichtorest the fixed legof the compass, which reduces the thickness of thepoints, and increases the'thickness of the roots. (See dotted lines L L,iig. l, plate l.)

The teeth in Williss system of gears are formed by the use of aninstrument called the odontgraph, iiomthe use of which the locus-centresand radii are derived.

By reference to fig. 2, plate 2, it will be seen that the pinion-teethare just as thick as they can be at the pitch-circle to work into therack. Now look at iig. 1- on same plate, where two such pinions aremeshed into each other, and an error or a lack occurs in which the teethdo not ill the opposing cavities by about T-l-U of an inch, a portion ofwhich is its error in angular velocity.

The same error will appear in any of the modifica tions of the Englishsystem, only to a greater degree than in Williss. y (Sue English, iigs.l and 2, plate l.)

In my system of gears, there are three peculiar and distinct features,neither of which has been used or claimed by any writer upon the subjectprevious to my invention.

'lhe irst of these features is, that the thickness of all teeth must bespaced at" right angles from the radial centre-line ofveach tooth, fromthe intersection of that line with the pitch-circle. (See B B, iigs. land 2, plate 5.)

'lhis feature, when properly used, will give a universal condition ofthickness, regardless of the curvayture of the pitch-circle, or ofradii, or locus-centres.

The second feature of my system is, that the meeting-point of the rootand point-faces is not at the pitchcircle, but inside of it, inproportion to the pitch and number of teeth. (This point will hereafterbe called the knuckle.)

By reference to dotted lines L L on iig. 1, plate 3, also L L, plates 4and 5, it will be seen that without this knuckle the teeth could neverbe tight in those positions; and referring to tooth A A of rack on iig.l, plate 3, it will be seen that without this feature ofthe knuckle K K,the tooth A A would not be in contact with either of the pinion-teeth,and that whichever was the driver, either rack or pinion, the operativepoints would be at M M, which is at an angle of twenty-two and a halfdegrees om the centre of motion, and the rack-tooth A A, which ought tobe doing nearly all the work inv this position, would, without thisfeature of the knuckle, be doing nothing; and similar to this will bethe result of all double-faced teeth that have their culminating pointsat the pitch-circle.

rlhe third feature of my system is, that the pinion which has the leastnumber of teeth in the set, determines and furnishes the radius forsweeping the faces of all the teeth that are included in that set.

The three points necessary for forming a segment of this circle arefound in thefollowing manner:

The point B BX, iig. 1, plate 3, and figs. l and 2, plates 4 and 5,indicating the thickness of teeth, as before described, is a fixedpoint.

. The second point of the segment is indicated at M Miig. 1, plate .3,and figs. l and 2, plate 4, which point cannot be deviated from andmaintain constant contact of the teeth.

For the third point of the segment, reference must be had to point C O,figs. l and. 2, plate 4, which is likewise a fixed point in the segmentof the circle which forms the faces'of the teeth; and from these threepoints are found the radius and locus-centre for the same.

For the obtaining of `the radius and locus-centres, reference must behad to the following rules and tables of coeiiicients:

Table of Coecients for Cfrandalls System of Gcars.-Ooe17cients forfinding Faces of Points.

f3 .2 e .2 B 2 .2 8 .e B 3 B .2 s 5 25 'E 5 Qi 5 5 5 si o' 8 e e' e o' ov o' 5 z 8 z z z z z r3 z z Rule for the above.

Multiply the coeicients in the table corresponding' to the number ofteeth by the pitch in inches and hundredths, and by the number lofteeth; the product will be in' lunulredths 0f an inch. This gives thedistance inside of the pitch-circle or line, for the pointface-loeus-centre line. All number of teeth above 200 to be calculatedas 200.

Oocgcent for jndi'ng the locus-centre line for faces o f yroots, thedistance outside of pitch-circle. Oce'ice'entjbr the distance outside ofpitch-knuckle, 24,00.

Iinside of pttch-muckle, 24,00. RULE-Multiply by pitch and divide by No.teeth.

Ans. in ths.

RULE-Multiply by pitch.

Ans. in 100tl1s. .Depth of rlmt of teeth, 32,500, Zeng/th of points,31,00. RULE-Multiplyby pitch.

Ans. in 100th`s.

RULE-Multiply by pitch.

E 1,85. Ans. in 100ths.

Rad/ias for sweeping faces of teeth., 61,75.

" Thickness of teeth at ptchJine for Ivery close gear, 40,0 Rm EMultiply by pitch ZI!- r I 1 For cast gea/rs, Vedwm 400 Ans. in 100ths.

ery open 48,0

NOTE-No teeth below fifteen in number can be strictly accurate.

At three-inch pitcln'the error of twelve teeth will be 3%, and ten teeth,46 of an inch.

the Locus-Centre Line fm' I disclaim any and all systems folforrning theteeth of gears that are usually termed involute, in which 'the faces 0fthe'teeth are formed with one continuous curve from point to root, andall systems which have not the three featmes which have been named anddescribed in my system.

What I claim as my invention, and 'desire to secure by Letters Patent,is-

1. The teeth of cog-wheels, for gearing, constructed as hereinbefere.described.

2. The thickness of the teeth spaced at right angles from the centreline of the same, substantially as set forth.

3. The meeting-point of the root and point-face circles inside 0f thepitch-circle, in accordance with the rules as specified.

4. The radii, for sweeping the faces of the teeth, obtainediiom thewheel containing` the least number of teeth in a set, as so described.

-Witnesses:v HORACE I. CRANDALL.

J AMES LYLE, WILLIAM E. TIRRELL.

